In some vapour compression systems an ejector is arranged in a refrigerant path, at a position downstream relative to a heat rejecting heat exchanger. Thereby refrigerant leaving the heat rejecting heat exchanger is supplied to a primary inlet of the ejector. Refrigerant leaving an evaporator of the vapour compression system may be supplied to a secondary inlet of the ejector.
An ejector is a type of pump which uses the Venturi effect to increase the pressure energy of fluid at a suction inlet (or secondary inlet) of the ejector by means of a motive fluid supplied to a motive inlet (or primary inlet) of the ejector. Thereby, arranging an ejector in the refrigerant path as described above will cause the refrigerant to perform work, and thereby the power consumption of the vapour compression system is reduced as compared to the situation where no ejector is provided.
An outlet of the ejector is normally connected to a receiver, in which liquid refrigerant is separated from gaseous refrigerant. The liquid part of the refrigerant is supplied to the evaporator, via an expansion device, and the gaseous part of the refrigerant may be supplied to a compressor unit. It is desirable to operate the vapour compression system in such a manner that as large a portion as possible of the refrigerant leaving the evaporator is supplied to the secondary inlet of the ejector, and the refrigerant supply to the compressor unit is primarily provided from the gaseous outlet of the receiver, because this is the most energy efficient way of operating the vapour compression system.
At high ambient temperatures, such as during the summer period, the temperature as well as the pressure of the refrigerant leaving the heat rejecting heat exchanger is relatively high. In this case the ejector performs well, and it is advantageous to supply all of the refrigerant leaving the evaporator to the secondary inlet of the ejector, and to supply gaseous refrigerant to the compressor unit from the receiver only, as described above. When the vapour compression system is operated in this manner, it is sometimes referred to as ‘summer mode’.
On the other hand, at low ambient temperatures, such as during the winter period, the temperature as well as the pressure of the refrigerant leaving the heat rejecting heat exchanger is relatively low. In this case the ejector is not performing well, and refrigerant leaving the evaporator is therefore often supplied to the compressor unit instead of to the secondary inlet of the ejector. When the vapour compression system is operated in this manner, it is sometimes referred to as ‘winter mode’. As described above, this is a less energy efficient way of operating the vapour compression system, and it is therefore desirable to operate the vapour compression system in the ‘summer mode’, i.e. with the ejector operating, at as low ambient temperatures as possible.
US 2012/0167601 A1 discloses an ejector cycle. A heat rejecting heat exchanger is coupled to a compressor to receive compressed refrigerant. An ejector has a primary inlet coupled to the heat rejecting heat exchanger, a secondary inlet and an outlet. A separator has an inlet coupled to the outlet of the ejector, a gas outlet and a liquid outlet. The system can be switched between first and second modes. In the first mode refrigerant leaving the heat absorbing heat exchanger is supplied to the secondary inlet of the ejector. In the second mode refrigerant leaving the heat absorbing heat exchanger is supplied to the compressor.